Excel 22 DXT

Hermann? Right, of course, it’s Hermann! It’s hard to say why I remembered his name as soon as he walked into the listening studio – like the man himself, it just resurfaced. We agreed that his last visit must have been almost 15 years ago, although I think just under 20 years is a more realistic guess. Back then, he had picked out my first transmission line with Seas equipment, which he had used happily and to his great satisfaction until just recently. But the teeth of time had been gnawing away at his loudspeakers too, and the surround material on the basses had been almost swallowed up. No, no, he wasn’t thinking of a repair – sometimes you have to let go of the old, even if you are very fond of it and always enjoyed its company. Nothing lasts forever, and new things have the great advantage of making it easier to break free from well-trodden paths. While good old groovy rock music was once the main musical element where he felt at home, recently he had started adding a little classical music to his faithful turntable, along with more and more jazz. “Of course, old age,” I reassured him. I had reached that point long ago myself. Of course, that was by no means the only reason to completely replace the box, because of course it could handle jazz and classical music too. Doris – hands down the best wife in the world, he said – had also wished for some smaller boxes, so he was happy to oblige. As a long-time reader of the magazine, he had been attracted to the smaller two-way speakers from the Blues class. But being used to large boxes, he was having trouble coming to terms with a membrane area that was almost cut in half. The big SB 18, Doppel 7 or Phase 34 would have helped, but those are free-standing boxes too. The compact version of the Kera 360.2 wasn’t really what Hermann considered compact. If we had one #20 instead of one #17 in a comparable-sized cabinet, with a sound level that could still handle the old rock music, that would be the box for him. Oh dear – I didn’t have anything like that on offer because it doesn’t really work. A #20 needs a certain amount of air volume, and it’s almost impossible to connect it to a tweeter because they can’t be separated out at a deep enough level. When Hermann left that day, I promised him I would work on fulfilling his completely understandable request.

Equipment

I spent the next few days working on data sheets and simulations for eight-inchers in dwarves’ houses, and I actually came up with a promising solution. Hermann had been used to the Seas sound for years, and all he wanted was a little more resolution and detail in the quiet and loud passages. The attentive reader will know that this is the very definition of the Blues class to which Hermann now belonged, in terms of his more sophisticated music needs. What could be more logical than seeking out the elusive box in its natural habitat in Europe, namely in Norway? The CA 22 RCY from the MS 4 TL was missing the last little bit of dynamicism, especially in a compact cabinet. Its big brother, the CA 22 RCX from the Power 220, was more promising there, but it needed at least 35 liters; placed on a stand, that pretty closely resembles the Kera 360.2. But the “better” version from the same company, Excel, lists the W 22 NY 0001 – a bass that’s right up my alley. It features a paper membrane and Nextel coating; every imaginable ventilation option, including under the raised centering bracket; an aluminum phase plug for heat removal; and short-circuit rings above and below the T-shaped pole core. The thick magnet is protected by a rubber rim, and the frequency curve on the Intertechnik side showed none of the spikes in the upper area that are common for metal membranes. Naturally I screwed the bass mid-range speaker to my measurement wall before gluing together a cabinet according to the data provided by the manufacturer.


Data sheet Excel W 22 NY 001

Part No.: 1381716

Measurements as a Zip-file





Equipment:


Parameters:


Measurements:

Frequency response and phase	Impedance	Frequency response under 0/ 30/ 60°
Distortion for 90 dB	Step response	Waterfall


Still, that didn’t solve my problem – finding an eight-inch bass mid-range speaker that works with 25 liters is only one side of the coin. Its large membrane creates too-high frequencies, which makes it almost impossible to connect the tweeter with a reasonable two-way system. There’s a good reason this combination is very hard to find on the market. A tweeter that is connected at 2 to 3 Hz radiates the sound in every direction, which produces a noticeable jump in the directivity index and leads to tonal discolorations when the listener is not located on the axis. What helps here is a wave guide, which is available from Dayton and P.Audio, for example. Since I’m not a fan of complicated building projects with uncertain results, I decided not to try putting one together myself with a saw and glue; it would never be easy to replicate, and it would lead to all kinds of follow-up questions if the box doesn’t sound right. The tweeter should be able to guide the wave right from the start, so I immediately thought of the Seas – with the longest name I’m capable of remembering: 27TBCD/ GB-DXT. I introduced it in the chassis test. I had already mentioned the improved connection to a large mid-range speaker using two steps in the front plate of the tweeter there, so now I was finally able to test the truth of my words in a practical application. Since almost three years have gone by since then, I took a couple more measurements of the living specimen to check the serial consistency of this Seas product. Any small deviations are naturally caused by measurement conditions that are not completely identical


Data sheet Seas 27TBCD/ GB-DXT

Part No.: 1381072

Measurements as a Zip-file

Equipment:

Parameters:


Measurements:

Frequency response and phase	Impedance	Frequency response under 0/ 30/ 60°
Distortion for 90 dB	Step response	Wasterfall


Cabinet

The little box for the W 22 NY 001 did not just need to be compact; it needed to be significantly smaller than 35 liters. When I said that 5/7 of that volume would do it, Hermann nodded at the other end of the telephone line, so I went ahead and had the wood cut to size at the hardware store. To add a little bit of color to my pictures, I used black MDF for the interior boards; I had beech multiplex cut to size for the sides. At this point, I’m no longer worried about cracks in the woodwork. A bigger problem is glued wood’s tendency to bend when it is only painted or oiled on one side. A milled groove all the way around helps to prevent that, by providing a larger gluing surface in two directions. I captured the creation and assembly process of the boxes in photos.



The rest of the assembly is self-explanatory – the glue is joint glue, and before anyone asks, no, I really didn’t use any screw clamps.



Before you go to the store, you will also need the dimensions of the boards. I included them in the construction plan, which I drew in SketchUp. If the two 2-D plans aren’t enough, you can also download the file in zip format here.



Cross over network

Separating loudspeakers close to their limits requires more than just one or two components per branch in order to create the right addition. Here, third-order filters were needed for both chassis elements just so they could hit the same notes in even a small range. For the W 22 NY 001, I also needed to compensate for the peak between 300 and 2000 Hz, which involved three more components in a suction circuit. I ignored the narrow dip around 850 Hz, probably caused by the membrane suspension and accepted by the chassis builder as a compromise for other benefits. I was able to skip a volume adjustment for the tweeter using a voltage divider. Its connection pulls it down to the level above 10 kHz, which is around 88 dB. The addition of the branches is fault-free if the bass and tweeter are connected out of phase..



At 88 dB of sound pressure and given the tonal standards I set for my Excel 22 DXT, smoothing the impedance for tube listeners was a basic requirement.



A common follow-up question from our do-it-yourselfers relates to building the crossover, which I like to glue to a wooden board. In this case it has two parts, so I took a picture to provide an easier explanation.

The last part of the documentation is also essential: installing the components in the cabinet.



Once they were assembled, I was able to measure the boxes as a finished product.

Frequency response and phase	Impedance	Frequency response under 0/ 30/ 60°
Dsitortion for 90 dB	Step responce	Watefall


Sound

When the boxes were finished, I called Hermann. He came right away, bringing Doris and a few records with him for a listening test. It was a good thing I had just set up a new little treasure in the store – two days earlier, Walter Fuchs had installed my Benz system with his best technical competency and measuring equipment. My new turntable was called “Destiny Incantare” – Thorsten Langer gave it to me in anticipation of my retirement, hopefully 20 years too early. 

We started with Neil Young’s “Harvest,” an album that is being reissued soon on vinyl, in an old-style design with rough cardboard on the outside and a glossy interior along with hand-written printed texts. The artist himself does not demonize the CD, but he does say that the small atmospheric sounds are reproduced more delicately on record. A good test of this was “Heart of Gold,” which confirmed the singer’s statement in a comparison with the silver disc; at the same time, it confirmed the dynamic skills of the Excel 22 DXT, which are unique to the Blues class. Hermann was smiling, and Doris took notice. “Meddle” by Pink Floyd was the next disc. It started off very calmly with “Echoes,” its floating vibrations completely freed in the deep space, and then moved on to more rock-based elements. The listener sitting in the middle wasn’t the only one who enjoyed it. Clean basses, bone-dry and clearly drawn, rang out on “Telegraph Road,” since Dire Straits and Knopfler’s distinctive voice were essential to this trip down memory lane. The increase in tonal quality compared to the previous box, which was by no means bad, was clearly reflected on Hermann’s face. “Beautiful!” said Doris, moved, when she heard Pavarotti sing “Nessun Dorma” as if it were the easiest thing in the world. No, we didn’t miss the mid-range speaker. The bass and tweeter had come together as a harmonic unit that didn’t need a third party.

When Doris and Hermann said their goodbyes a couple of hours later, they were both beaming. They had found a compromise between box size and space constraints that made them both happy. “Of course, I would have let him build some big boxes too if the little ones didn’t work,” Doris said to me as they left.

Technology Excel 22 DXT




In case you want to build this kit by yourself all components are available from Intertechnik.